Ah-HA!

Many many years ago, I spent a few summers in a row going off to Girl Scout Camp. One summer, at twilight, the counselors herded us all into one of the big tents and pushed some candy in our hands, with orders to wait to eat it until everyone was--and no sucking (shut up!), we were supposed to chew on them.

Since it was dark inside the tent, we had no idea what they'd pushed into our hands at first, but it turned out to be a life saver.

On cue, when we were told, we all popped the things into our mouths and chewed. Imagine my surprise when there were sparks of light all over the tent! I have never, ever forgotten what that looked like.

Turns out, it wasn't anything weird that they'd added to the candy after all--it really happens with wintergreen lifesavers.

Check it out: http://science.howstuffworks.com/question505.htm